1. Field of the Invention
This invention relates to a reel for a web such as tape, and more particularly, is directed to a tape reel for tape cassette whereon a magnetic tape is wound, the tape cassette being of the type used on magnetic video tape recording and/or reproducing apparatus.
2. Description of the Prior Art
An example of a conventional tape reel for use with a video tape recorder includes a flange and a reel hub which are formed of synthetic resin and integrally molded with each other, thereby forming a so-called "one-flange type" reel. A sub-flange is connected to the other, free end of the hub. The diameter of the sub-flange is smaller than that of the integral flange. The connection of the sub-flange and the hub is as follows. An annular projection of the sub-flange is received in an annular recess which is formed in a hollow portion of the free end of the hub adjacent to a rib which substantially closes off the opening of the end of the hub. Then, the projection on the sub-flange and the recess at the free end of the hub are connected to each other by ultrasonic welding. The tape reel as constructed above becomes deformed by the contraction of the material when the tape reel is merely left to sit for some length of time after the welding. That is, the diameter of the top end of the reel hub becomes large as compared with the diameter of the other end which is reinforced with the rib. Accordingly, a magnetic tape wound on the reel has a tendency to protrude outwards in the radial direction, and will develop a permanent set due to the thermal contraction or the stress of magnetic tape. Hence, the magnetic tape sustains relatively high tension near the upper edge of the tape in the direction across its width. The magnetic tape withdrawn from the reel has an undulating shape like that of "wakame" seaweed, because the upper side edge of the magnetic tape is elongated in respect to the lower side edge thereof. Such magnetic tape will not be able to maintain stable contact with a head drum of a video tape recorder. A special problem occurs when the upper side of the magnetic tape is used as an control track. In such case the recording or reproducing of the control signal by magnetic heads becomes unreliable, causing syncronization errors, and also causing the S/N ratio to fall especially in the lower portion of the reproduced picture.